Communication and detection system



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COMMUNICATION AND DETECTION SYSTEM Filed Sept. 12, 1931 B-E-B-I 7 Sheets-Sheet 2 ENERGY FREQ.

A -F-:- b r' 'i' fi I HJ-rD-fi 1 |m||| RESPONSE 9 0 2/ BEL-Q I Iq/Z 2 j IIYVE/VTOR. /7 Herman Putts M11121, Jr. Mw/FWM ATTORNEY 250. RADMNT EN'LMJ! March 1936' H. P. MILLER. JR

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H. P. MILLER. JR 2,032,588 COMMUNICATION AND DETECTION SYSTEM Filed Sept. 12, 1931 7 Shuts-Sheet 5 I TEMP. /93 m6 CONTROL H59 5 I /97 DEVICE 1 94 J RECEIVER EEG-Eb Hermag Pufls Miller, Jr.

March 3, 1936. p M1LLER, JR 2,032,588

COMMUNICATION AND DETECTION SYSTEM Filed Sept. 12, 1931 7 Sheets-Sheet 6 lNVEA-TOR.

Herman Putts Miller, III- A TTORNLY Z5U. KAUIAM LN Lnua March 3, 1936.

H. P. MILLER. JR

COMMUNICATION AND DETECTION SYSTEM Filed Sept. 12, 1931 QEXCITATION 0 souszca a EXCITATIONO sourzca 4* 7 Sheets-Sheet 7 QEXCITATION ,1 souxzcs s30 Allllllllllkaa size J54 357 352 365 2 3 /2 366 5% 5 AMP g gg REC QEP E 2. LE

/.'\/'V1VTOR. Herman Putts Mlller', Jr.

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Patented Mar. s; 1936 UNITED STATES PATENT OFFICE COMMUNICATION AND DETECTION SYSTEM This invention relates to communication and detection systems and particularly to such systems utilizing extremely high frequency waves such as light and heat waves as the medium of transmission.

Light as a medium of communication between persons has been employed in various systems well known in the art such as the heliograph and other systems employing 81W- Ms. Although a vantages of using certain 'ght frequencies are many, the results obtained by the old methods have not been entirely successful because of inetlicient detecting apparatus. The art of light signalling was neglected during the development of radio communication, but at present radio has failed to meet present day exigencies such as freedom from static, directional concentration. and the ability to replace direct vision. The present invention provides, therefore, a communication system having these desirable features, the system including transmitting and detecting apparatus in accordance with the disclosure hereinafter.

5 An object of this invention is to communicate between separated points utilizing wave radiations as the medium of transmission.

Another object-offhe invention is "to" com= municate between separated positions utilizing a wave radiations in the visible and invisible spectrums.

A further object of the invention is to accurately and efficiently detect the presence and determine the frequency of radiations projected by known and unknown sources.

The present invention particularly contemplates a method of and means for visibly detecting invisible light waves in both the infrared and ultra-violet spectrums. It utilizes the 4d ability of certain radiated waves to penetrate moisture and dust laden atmospheres under all atmospheric conditions. the detection of these waves being a particular feature of the invention. In brief, the detection is accomplished by combining light waves from a source of any desired frequency with those from another source to form waves of an entirely different frequency and preferably of a frequency within the visible light range. In the heterodyne radio receiver it so is well known how an incoming radio wave may be combined in a resonant circuit with a local radio frequency to produce a third frequency which may or may not be audible. In effect. the present invention discloses means for producing the same results with light waves,

A similar phenomenon has long been known in color photography conceived by Lippmann in which standing light waves produce lamina: in a sensitized film which, when developed and viewed in reflected light. produces the original colors. With this system, the combination of two light waves of different frequencies has resulted in a variation in intensity of the lamina: in the film in accordance with a third frequency, this frequency checking previous calculations.

My invention, however, combines two light frequencies to form a third frequency by employing the phenomenon known as scattering with change in frequency". It is known in the art that when monochromatic light of a visible frequency is scattered" by certain liquids or gases or reflected by crystalline substances and then observed with a spectmscope, it is possible to oberve lines representing frequencies other than that of the original light. This has been explained as being due to the change in size of the quanta given off by the light source. If the quanta give up some of their energy to atoms in the molecules of the "scattering" or reflecting medium. they are scattered" with a lower frequency. while if they receive energy from the medium they are "scattered" with a higher frequency. The frequency differences between the incident light waves and the scattered" light waves have been found equal to light frequencies which are in the infra-red spectrum.

In applying the principles mentioned above, the molecular atoms of the "scattering" medium are either energized or deenergized by invisible radiations. when light waves of another frequency are reflected by the same medium, a portion of these light waves are shifted to a third frequency and have an intensity which is dependent upon the degree of excitation of the medium by the invisible radiations. The shifted light waves may have a frequency in the visible spectrum and may be detected with well known light sensitive instruments. Shifted light waves which have been previously modulated may be detected in any well known manner such as by heterodyning or any radio detecting method.

Although a third frequency is obtainable by combining any two different light frequencies in accordance with the principles of my invention, more eilicient combination may be effected by producing more in-phase components of the combining waves. It is well known in the art that light from incandescent solids and gases consists of discontinuous trains of waves the lengths of which depend on the time required for an electron in a light radiating atom to pass from one energy state to another, or approximately 10- seconds. With the energizing sources commonly used, these wave trains may start at irregular intervals so that the waves received at a given point may not all be in-phase. By exciting a light source with a radio frequency current, the period of which is comparable with the time required for an electron to pass from one energy state to another, or 10- seconds, more wave trains will be started in-phase and more efficient combination of two different light frequencies will be possible. Still greater efficiency may be obtained by the selection of the light frequencies in a manner to be described. Radio frequency currents with a period of 10- seconds, or a wave length of 3 meters, may be readily obtained either in the form of damped, undamped. or pulsating waves, or as harmonics from a radio frequency source of higher wave length.

This method of exciting the light sources permits the accomplishing of other results which are disclosed hereinafter. among which are the modulation of the invisible radiations in any well known manner and the making of such modulations readily understandable at the receiving point.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself. however, both as to its organization and its method of operation. together with additional objects and advantages thereof, will best be understood from the following description of certain specific embodiments, when read in connection with the accompanying drawings in which like reference characters represent like elements and in which:

Fig. l is a frequency and wave length chart of the waves utilized in my invention; Fig. 2 shows curves illustrating the principle of scattering with change in frequency; Figs. 3 and 4 show schematically two methods by which scattering with change in frequency" can be obtained; and Fig. 5 shows diagrammatically the elements used in my invention for a light communication system.

Figs. 6a and 6b are schematic drawings of a transmitter and receiver, respectively, for a com munication system in accordance with my invention; and Fig. '7 is an elevation of the light source used in the transmitter of Fig. 6a.

Figs. 8a and 8b are schematic drawings of a transmitter and receiver, respectively, of another embodiment of my invention.

Figs. 9a and 9b are schematic drawings of a transmitter and receiver, respectively, in accordance with the principles of my invention and having temperature control for the receiver scattering medium: and Fig. 1D is an elevation of the particular light source used in the transmitter of Fig. 9a.

Figs. 11a and 11b are schematic drawings of a communication system embodying the principles of my invention and having self oscillating light sources; Fig. 12 is an elevation of the light source Referring to Fig. 1, a frequency and wave length chart shows the range of radiations which may be used for communication purposes including those employed in accordance with my invention. The radio range has been considered to lie between 1.3x10 and 8.6)(10 cycles per second; the infra-red between 8.6x 10 and 4.0 x 10 cycles per second; and the visible spectrum between 4.0 10 and 7.9)(10 cycles per second. The following description discloses methods of and means for utilizing all light frequencies. both visible and invisible, for communication purposes. However, the following disclosure describes particularly communication systems employing invisible frequencies, such as infra-red, for transmission purposes since visible and the higher frequencies shown on the chart are readily absorbed by material objects.

Reviewing the method of modulation employed for radio transmission and reception, it is well known that the energy radiated from a radio telephone transmitting station operating on a frequency A varies with frequency in the manner shown by curve "a in Fig. 2, in which A is the carrier frequency and B a modulating frequency causing two peaks at A+B and A-B. With A a radio frequency and B an audio frequency, the beat frequencies will be radio frequencies, but if B is also a radio frequency of nearly the same value as A one of the beat frequencies will be audible as in the heterodyne receiver.

A phenomenon similar to modulation has been observed with light waves using a portion of the apparatus shown in Fig. 3 in which 8 is an are light energized by an energy source 9, but which may be any suitable type of source of wave energy in the visible or ultra-violet regions. Light from are 8 is collected by a reflector I0 and passed through a condensing lens I I from which it proceeds in a parallel beam through a light filter l2 into a liquid or gas or combinations of different liquids or of different gases l3 capable of causing scattering with change in frequency", such scattering being obtained with benzene, carbon tetrachloride, carbon dioxide, or the like. The "scattering medium 13 may be maintained at any suitable temperature and pressure. The filter I2 may be comprised of one or more of the well-known forms of liquid cell, glass, or gelatin filters, or combinations thereof. selected in a manner to be described hereinafter to permit light of practically one frequency to pass into the medium l3. A container H for the medium I3 has attached to a face at right angles to the axis of the light beam from light 8 an extension containing a lens-l5 which focuses a spot in the medium I3 on a. slit I6 of a spectrometer containing a dispersing prism l1 and a photographic plate l8. A second are light I9 which may be any suitable type of source of radiations that will excite to vibration the molecular atoms in the medium l3, and which is energized by an energy source 20 through a switch 2|, is supported on an extension to the container 14 and in line with the light beam from arc light 8. Light from I9 is collected by a reflector 22 and brought to a. parallel beam, which is coaxial with the beam from light 8, by condensing lens 23 before passing through a light filter 24 into the medium I3. The reflector 22 may be of copper, zinc, or some material that will readily reflect the radiations employed from arc light I9. but will reflect with low efficiency light of the frequency passed by the filter l2. The lens 23 may be of glass. quartz, fluorite. rock salt, sylvite or any other material capable of passing the employed radiations from light l9, while filter 24 may be a combination of one or more of these substances with one or more substances that will also absorb radiations of the frequency passed by the filter If. The absorbing substances may comprise liquid or gelatin films or coloring matter for the non-absorbing substances mentioned above. A specific selection for a practical application is given hereinbelow.

In Fig. 4 a similar system is shown. elements similar to those in Fig. 3 being given like reference characters. In this system. however. the two light beams from lights 8 and I9 are not directed toward each other but are superimposed by means of a filter-reflector 25 which is of a material that will readily pass the visible light from light 8. but will reflect the invisible light from light l9. Reflectors of this type can be obtained in certain kinds of colored filter and heat transmitting glasses. it generally being the case that a glass giving a low transmission at a particuar light frequency is a good reflector at that frequency. The superimposed light beams are directed toward a crystalline plate 26 which may be of any substance capable of causing scattering with change in frequency", such as quartz and the like. The plate 26 then reflects the beams of shifted frequency into the lens ii. In this particular system the eflect of "scattering with change in frequency" may be a more coherent reflection than is obtained with that shown in Fig. 3.

This phenomenon has been observed with the use of the apparatus of Figs. 3 and 4 without the aid of the light IS. the filter-reflector 25. and the elements associated therewith. the latter elements and their use being a feature of my invention. The phenomenon which has been obtained with the former apparatus is a spectroscopic image on plate It of the form shown at "b" in Fig. 2. This image contains one line C for the wave frequency of the light from are 8 and six additional lines at frequencies C+D, CD. C-l-E, CE, C+F, and CF. These six lines indicate the same effect as the modulation of frequency C by frequencies D. E. and F. The frequency differences D. E, and F have been found to vary with the scattering medium used.

The explanation given for scattering with change in frequcncy" is that some of the light quanta from are 8. in Figs. 3 and 4 for instance. have their energy content changed by collision with molecules of the medium I3 or of the crystalline plate 26 and either give up or receive a small amount of energy from the atoms in these molecules. Since the energy in a light quantum is given by the expression ho, where h is a constant and 27 is the frequency. a change in energy must be accompanied by a change in frequency. If energy is given up. the frequency will be decreased and if energy is received. the frequency will be increased. Since the energy changes occur in fixed amounts one way or the other. the frequency shifts above or below the original frequency C occur in pairs as shown in "b" of Fig. 2. These frequency shifts are usually small so that if the original frequency lies within the visible spectrum the shifted frequencies will also be visible. and the frequency shifts being small, are of the order of magnitude of the frequencies found in the infra-red spectrum. (See Fig. l.) The general effect is. therefore. that of modulation of a visible frequency by an infra-red frequency. It is also found that small frequency shifts are easier to obtain than larger ones. this being a very desirable feature since the low infra-red frequencies are at the present time least understood and harder to use for communication purposes while the higher frequencies have been used to a limited extent.

Another phenomenon observed is that it is easier to obtain spectrum photographs showing shifts to lower frequencies than to higher ones. This is explained by the theory that light quanta of the original frequency give up some of their energy to the atoms in the "scattering" or reflecting medium more readily than they receive energy. In order for these light quanta to receive energy from the atoms. it is necessary for the atoms to be set in vibration by some other means. This has been done by beating the "scatterlng" or refle;ting medium and has caused increased intensities of the shifted light waves of higher frequencies. Since heat waves lie in the infra-red spectrum. the projection of infra-red waves on the medium produces the same effect as heating.

My method of and means for setting up vibrations in the "scattering" mediums l3 and 2B in Figs. 3 and 4 is the are light I! and the elements associated therewith. The light beam from this are is of such a frequency that it sets up vibrations in the atoms of the scattering medium with the result that the intensity of one of the lines in the spectrum photograph. such as the (2+5 line at "b" in Pig. 2, is considerably increased; Interrupting the energization of the are light l8 by opening and closing the switch 2| will cause corresponding changes in the intensity of the C+E line. By also inserting between lens l5 and aperture li a light fllter of the same general type as filter l2 which will pass only light of frequency C+E, the variation in intensity of the 0+3 line due to the manipulation of switch 2| will be more readily observed.

The use of scattering with change in frequency" for the detection of invisible radiations is not to be confused with methods employing the well-known phenomena of fluorescence and phosphorescence. A medium exhibiting these phenomena is characterized by its ability to absorb light over a band of frequencies in the ultraviolet spectrum and in the ultra-violet end of the visible spectrum. A frequency within this absorption band causes the medium to fluoresce and emit light over a broad band of still lower 1 frequencies than those in the absorption band. Since the fluorescent band is usually within the visible spectrum. this phenomenon permits the visible detection of invisible ultra-violet frequencies without the use of a third source of light frequencies. Phosphorescence may be employed for the detection of infra-red frequencies through the quenching action of such frequencies. In this case a local source of light vibrations of frequency C may cause a medium to phosphoresce over a relatively broad band of lower frequency. such as CD to C-F, and the infra-red vibrations are mereby employed to stop phosphorescence. In my invention the "scattering medium may not have the absorption band characteristic of fluorescent mediums and the light of shifted frequency may be monochromatic light of a higher frequent; such as 0+5. The variation in intensity will vary directly with the intensity of the infra-red vibrations and not inversely as in the case of phosphorescence.

The systems of Figs. 3 and 4 also permit measuring the frequency of invisible radiations. such as from the arc light i9. If the filter 24 is selected so that it will pass all radiations below the frequency passed by the filter i2, radiations of a number of frequencies from the light I! will strike themedium i3or2i. Thismayresultina change in the intensity of some of the shifted lines on photographic plate II. For example, the C+D and 0+! lines in b" of Fig. 2 may have greater intensity than they would if light I! were not used. This would indicate that the light 19 emits radiations corresponding to the frequency shifts D and F. Since the frequency C from light 8 can be accurately measured, the frequencies of the radiations from light it may be determined from the image on the photographic plate It. In the same manner, other radiations from light I! may be measured by using a scattering" medium which causes other frequency shifts. The amount of change in the intensities of the lines on the plate It will also indicate the intensity of the radiations being measured.

Referring to Fig. 5, the general manner in which the above described principles are applied for communication purposes in my invention is shown schematical'y. In this drawing a transmitting light source 2'! is capable of radiating one or more infra-red or invisible waves of a frequenzy that will readily pass through a fog or dust laden atmosphere. This light source is energized to the desired intensity with any suitable form of energy, such as an alternating, direct, or pulsating current from an excitation source 28. The intensity of the excitation applied to the light source 21 by the exciting source 28 may be controlled in accordance with a modulating source 29. which may be a telegraph key, sound waves, television signals, or any other source of modulations of a like nature.

Radiations from the light source 21 are collected by transmitting reflector 30 which is of a suitable material and form to eiflciently direct the radiations to a receiving reflector ll of the same or of a diflerent material and form, preferably, however, of the paraboloidal type. It is to be understood that reflectors are employed to increase the efliciency of the system, but may be dispensed with in some cases. After being intercepted by the reflector 3|, the radiations are again collected and brought to a small parallel beam with a small reflector 32. which may be of the same material and form as the reflector Ii or may be of a material, such as copper or zinc, which will readily reflect the infra-red or invisible waves from the source 21, but will reflect very poorly any visible waves from sources close to the reflector 3i. The rays are then directed through an opening in reflector 3| to a. plane reflecting mirror 33 of the same or of a diiferent material from reflector 32 which is placed at an angle suitable for directing the small parallel beam towards one face of a container 84 containing a medium capable of producing scattering with change in frequency". A second or local light source 35, preferably of the same general type and form as the light 21, is energized by an exciting source 36, which may be of the same type as source 18, producing a light beam of visible or near visible frequency which is directed towards another face of the container 34. A light sensitive cell 31 of a type giving maximum response at a shifted light frequency, such as C+E, is placed with reference to container 34 so that it receives the maximum eflect of the light waves of frequency C+E. The variations in current through the celljl are impressed on a suitable receiver 38 arranged to function with the type of variations received, whether they be direct current impulses, modulations of a high frequency carrier wave, or radio telegraph signals. and which changes these variations to a form that can be ratdily heard or observed through the medium of a reproducing device 39. The device 38 may be a telephone receiver. loud speaker, automatic recording device, television system or any similar device or system.

In the operation of the system of Fig. 5 signals of whatever form desired are impressed by the modulating source 29 on the excitation source 28 and cause intensity variations in the infra-red radiations emitted by the light source 21. Whenever these infra-red signals strike the medium in container 84 and excite some atoms in it, light waves of frequency C from the visible light source 35 are shifted to a higher frequency 0+2. The intensity of the shifted light falling on the light sensitive cell 31, therefore, varies in accordance with the signals from the modulating source 29. The light sensitive cell 31 may have a frequency response corresponding to curve c" in Fig. 2, in which case light of frequency C+E gives maximum response while the original light frequency C gives little response. Any other shifted frequencies will be too weak to have any appreciable efl'ect. The response of cell 31 will then vary between a value 0 on curve 0" when there is no infra-red signal and a value P when the infra-red signal is maximum. This variation may be amplified and detected in the receiver 38 and interpreted with the reproducing device 39. For maximum response in cell 3'! it is desirable that the excitation sources 28 and 36 be adjusted. by means described hereinafter, so that the two light beams striking the scattering" medium in the container 34 cooperate efliciently. To obtain two-way communication it is only necessary to associate two one-way systems, or use the same apparatus but employ two different transmitting frequencies.

The general principles of the invention and their general application have been described above and I now refer to speciflc preferred embodiments each of which has its particular advantages as will be set forth hereinafter.

In Figs. 8a and 6b, a complete light wave communication system is illustrated in which the light sources are excited with alternating currents, Fig. 60 being the transmitter and Fig. 6b the receiving equipment. The reflectors. or radiation projectors, and optical system are similar to those in Fig. 5, reflectors 40, ll, 42, and 43 corresponding to reflectors 30, 3|, 32, and 33 of Pig. 5 and operating in a similar manner. A transmitting light source 45 of the gas discharge type containing a gas such as neon. helium. or mercury vapor, is positioned at the focus of reflector 40, the reflector being constructed to project a parallel beam from such a source. This light source is shown in annular form and may have a gas pressure giving a long positive column but may vary in these respects. the prime requisite being the concentration of a maximum wave radiation toward the receiver with a given amount of input energy. The side elevation of light source I! is shown in Fig. 7. electrodes 46 of copper, aluminum, or similar material being located at the lower extensions of the annular tube of optical or heat transmitting glass. quartz. or any suitable material which is transparent to the radiations to be employed.

The excitation source for light 45 shown schematically at 41 in Fig. 6a is of a well known type of feed-back oscillator comprising a vacuum tube 48, grid choke coil 40, grid inductor 50, feed-back inductor 5i, plate circuit inductor 52, plate circuit condenser 53. choke coil 54, and by-pass condenser 55. A source of direct current potential 56 supplies the vacuum tube 48 with anode voltage as well as energy to maintain light source at minimum intensity when the circuit 41 is not oscillating. The light source 45 is connected to the excitation source 41 over conductors 51 and 58.

In series with conductor 58 is a condenser 59 of low reactance. In parallel with condenser 59 is a suitable potentiometer comprising the variable resistance arms and SI. arm 50 being capable of adJusting the direct current flowing through the light 45 when the circuit is not osciliating, and arm 5| together with arm 50 being capable of suitably adjusting the direct current through the light 45 when the circuit is oscillating. The total resistance of arms 60 and Si may be large in comparison with the reactance of condenser 59 at the oscillating frequency. Arm 5| is also connected between a moving arm 62 and a back contact 63 of a relay 64. The relay 54 is energized from an energy source through a suitable signalling device 56 which is shown as a telegraph key but may be any style of manually or automatically operated make and break device. A front contact 61 and the arm 62 of the relay 54 are connected to the ends of the grid choke coil 49.

In the operation of the transmitter shown in Fig. 6a, the closing of the signalling device 66 operates relay 64 and brings arm 62 in contact with contact 61. This shorts the grid choke coil 48 and permits the circuit to oscillate at a suitable frequency. An alternating current then passes through feed-back inductor 5|, plate circuit inductor 52, conductor 51, light source 45, conductor 58, condenser 59, and condenser 55. The value of this alternating current may be adjusted by means of the tapping connection between conductor 51 and inductor 52 to a value that will give light radiations of the frequency and intensity desired. A small direct current also passes from the energy source 56 through choke coil 54, feed-back inductor 5|, plate circuit inductor 52. conductor 57, light source 45, conductor 58, and resistors and 5!. While this direct current may have any desired value, it is preferably small in comparison with the alternating current through the light source 45. when signalling device 56 is opened. relay 54 is lie-energized and the short across choke coil 49 removed so that the circuit does not oscillate and no alternating current flows through the light source 45. At the same time relay arm 52 touches contact 53 and shorts the resistor 5| permitting the direct current through the light 45 to be djusted by the resistor 60 to the value that will just maintain the discharge in light 45. This keeps the gas in light 45 in an excited condition at all times, thus accelerating its illumination when the oscillations are started and stabilizing the load on the oscillator. The light waves given off by the light 45 during the non-oscillating periods are of such low intensities and have such irregular wave trains as to .cause little effect on the distant receiving apparatus. The usable light waves sent out by the transmitting system will. therefore. vary in intensity in accordance with the operation of the signalling device 66.

In the receiving system of Fig. 6b. a local light source 61 lsaspectrumtubeofthel-itypebut maybeanyformofdlschargetubecapableof providing a concentrated source of light of the desired intensity and frequency. This source 87 may be energized by any suitable source of alternating current of the desired frequency, such as a feed-back type of vacuum tube oscillator 68 acting through conductors is and 10. The oscillator i8 issimilarinmostrespectstothe oscillater 47 in Fig. 6a and the elements in 58 which aresimilartothoseinfl havebeengivenlike reference characters with prime indicators. A source of direct current potential 1| supplies the vacuum tube 48' with anode voltage which may bevariedoverthedesiredrange bymeansofa suitable potentiometer 12. In conductor 69 is a condenser 13 suitable for adjusting the phase of the current through the light source 51.

Light from the source 61 passes through a plurality of holes 14 in a disk 15, the holes 14 being spaced so that. when the disk is rotated at a suitable speed by a prime mover 75, the light from source 61 is interrupted at an audible frequency. After passing through the holes 14, the light from source 61 is brought to a parallel beam by condensing lenses 11 a light filter 18 which admits only light of the desired frequency into a "scattering" medium 19. The medium 79 may be a solid. liquid, or gas capable of causing scattering with change in frequency" and maintained at suitable temperature and pressure. Radiations from the transmitting source 45 of Fig. 6a are reflected by the reflector 43 through a light filter 80 into the medium 79 in the manner described hereinabove. The light filter 80 passes only one or more invisible radiations of the frequencies which it is desired to use.

A lens 8| focuses a spot 82. of suitable size and position in the medium I! to give the maximum amount of light of shifted frequency, onto a light sensitve cell 83 through a light filter U4. The light filter 84 may be capable of passing light of the shifted frequency without passing any light from the beams entering the medium 19 through the filters 18 and 80.

Specifically the tube 51 may contain helium gas giving a strong radiation at 0.5876 mcron. The filter Il may then be an orange filter glass which will not transmit any of the visible radiations from source 61 below 0.5876 micron. The radiations utilized in the transmitting source 45 may have a wave length of approximately 3 microns. such as may be obtained from a strontium arc. The reflectors 42 and 43 may then be of zinc and the filter 80 of quartz thus permitting radiations of 3 microns to enter the scattering" medium I8 without permitting visible radiations to enter. Another possible arrangement is to use a red heat transmitting glas for the filter 80. Such a filter transmits radiations of 3 microns but does not transmit radiations below 0.7 micron.

The scattering" medium I! may consist of a substance such as phenol, dipentene, dimethylanline, or any substance giving the necessary frequency shift E. Using phenol the shifted frequency C+E would have a wave length of 0.4981 micron. The filter 84 may. therefore. consist of a suitable didymium filter glass together with a glass filter cell 2 centimeters thick containing a 5% solution of copper acetate in water. The didvmlum filter read ly transmits radiations at 0.4981 micron but not at 0.5876 micron while the copper acetate solution absorbs radiations above 0.6 micron. The radiations falling on the photoelectric cell 83 will have a wave length in the before passing through ndghborhood of 0.5 micron. This cell may,therefore, employ a photo-unissive surface of strontium. barium. or rubidium. Combinations of other similar elements will be readily apparent to those skilled in the art.

Current variations through the cell it are madetooperateareproducingdevicelibymuns of a suitable receiver, such as the well known non-oscillating type of radio receiver shown schematically at N. This receiver comprises vacuum tubes I1 and II, input resistor l9, plate circuit inductor 80, grid circuit inductor ll, grid condenser 12, grid leak resistor 03, and by-pass condenser II. The receiver is connected to cell i! through conductors I5 and 86. In conductor 05 is a source of direct current potential l! for the cell 83 while in conductor is an inductor it suitable for introducing an alternating potential from the output circuit of the cell 03 into the grid inductor ill of the oscillator 68.

In the operation of the receiving system shown in Fig. 6b, the oscillator $8 may be tuned by means of condenser 53' to the same frequency as the oscillator 41 of Fig. 6a and the intensity of light from source 1 adjusted by varying the anode potential of tube 48' with the potentiometer 12. It will be realized, however, that since the oscillators 41 and i8 modulate the light beams from sources 5 and i! at an alternating frequency which may lie in the radio spectrum, in order to obtain a maximum response from the cell 83 it is desirable to have the modulated light waves arrive at the "scattering" edlurn II with the modulations in-phase. The two sources 15 and 1 may necessarily be located at different distances from the medium I! so that for maximum response the phase difference between the alternating currents in the lights 45 and 61 may have to be adjusted to produce this in-phase relationship in the medium 19. Since the gas discharge in the light 6! acts as a pure resistance, the necessary phase adjustment may be obtained with the variable condenser 13 and the variable tapping connection between condenser 13 and the plate inductor 52'.

Another desirable adjustment is to make the oscillation frequency of the circuits 4'! and it of such a value as to encourage the emission of trains of light waves from the light sources 45 and 51 at periodic intervals which are preferably multiples of the periods of the light waves being used. With direct current excitation of the light sources 45 and $1, the wave trains would be emitted at irregular intervals and the phase of the waves reaching a given point would, therefore, be constantly changing. By exciting the sources with alternating currents. more of the wave trains willstartoutwhenthecurrentsareatthelr maximum points and hence more of the waves will reach a given point in-phase. In order, however, for this effect to be most noticeable, the frequency of the alternating currents should be higher than those ordinarily used and preferably comparable with the frequency at which an electron in a light radiating atom can periodically change back and forth between two energy states. It is known that such an electron can pass from one energy state to another in approximately 10- seconds so that the total time required for an electron to make a complete change would be approximately 2x 10- seconds. corresponding to a frequency of 5x10 cycles per second. or a wavelength of 6 meters. The exciting sources should, therefore. preferably deliver electrical impulses to the light sources at the rate of approximately 5x10 impulses per-second. with the rate of e!- eitation a multiple of the light frequency. there is lesschanceforachangemphase between succeasive wave trains and hence more of the light waves from each light source arrive at one point in-phase. when the two light sources 45 and 6'! are excited at the same trequency. in order for the rate of excitation to be a multiple of the light frequency for both sources it would be necessary for the frequency of one light wave to be a multiple of the other. It should be noted. however, that the above described frequency adjustment merely serves to increase the efficiency of the communication system of rigs. 6a and 6b and is not a requirement for its proper functioning.

It is also desirable in this embodiment of my invention to maintain the same phase relationship between the currents in the two light sources 45 and 81 while signalling. The oscillating circuit it functions without interruptions while the oscillations in circuit 47 are started and stopped in accordance with the signalling device 66. Without some special control means there is no assurance that their phase relationship will remain used. In order to maintain this phase relationshlp, the coupling between grid inductor ill and feed-back inductor Si is adjusted to a value that will permit feeble oscillations. These oscillations are just sumcient to cause light from source 61 to be "scattered" by the incoming radiations from light 5. even though the two light modulations may not be in-phase in the medium 18. The light of shifted frequency in the medium ll causes a small alternating current to ilow through the cell '3. conductor 85, potential source ll. ruistor ll, inductor i8. and conductor 86. This current through inductor ll induces a controlling voltage in the grid inductor it which may be out of phase with the small feed-back voltage induced in inductor 50' by the current in inductor II. The controlling voltage quickly pulls the feedback voltage into phase with it and the two voltages combine to give stronger oscillations in the circuit 68. This increases the excitation of the light 1 and. up to a certain point, the current through the cell It. the controlling and feed-back voltages on tubes 48'. and the alternating current in the circuit 8. This feed-back effect from the oscillator back-through the light 1 and the cell .3

will also tend to maintain the same frequency of oscillation in the circuit 88 as in the circuit 41. In other words, I utilise the principle that causes two oscillators at approximately the same frequency to pull into step.

The rotating disk It with its holes 14 interrupts the light beam from light 61 so that with a continuous dash signal coming in from light 45 the intensity of the light of shifted frequency will vary at a frequency determined by the frequency of interruption of the light from source 61. The light cell ll, therefore. has three variations in the intensity of the light impressed upon it: an alternating frequency due to the oscillators l1 and a. an audio frequency due to the rotating disk 15. and a signalling variation due to the signalling device 66. These variations cause a current to how from the 'cell 83 through conductor Ii. potential source l1, resistor IO, inductor I, and conductor IS. The variations in this current are impressed upon the grid of the tube II by the voltage drop in resistor 88, are amplified by the tube I! and its associated elements and rectified by the tube ll and its associated elements in the well known manner. Because of the audio frequency varianot pass through the prism 2 unless the elections. the signals impressed on the reproducing trodes I08 have been energized by the source I09. device 05 will be audible signals in accordance The radiations projected from the reflector I with the signals sent out from the transmitting l. h r e, v ry in in e y in mordan system. with the control of the modulating source IIO In Figs. 8a and 8b is shown another complete 'Ihese radiations will be more uniform than light wave communication system in which the light sources are located at a distance from the reflector system and are excited with pulsating l0 light source an light beam from light plane of polarization has sistor I23.

reflectors I00, IOI, and operate in a manner similar to reflectors 30. II, 32, and 22 of Fig. 5. For the transmitting are light I05 is shown in Fig. 8a, of light may be used that will give tained will depend on the trodes employed. By means of an ellipsoidal reflector I05, the light beam from light I05 is brought to a focus at the center of a Kerr cell I01.

a modulating source IIO. Along the axis of the I05 and on either side of the Kerr cell I01 are a polarizing prism III and an analyzing prism H2, so placed with reference to each other that light from light I05 will not pass through both of them unless the been changed by the energization of the electrodes I08. After passing through the prism I I 2, the light beam is made parallel by a suitable paraboloidal reflector II: and projected over a desired distance to a plane reflector H4. The beam is then reflected from reflector II4 through an opening in the reflector I00 to a small paraboloidal reflector II5 which distributes the beam over the surface of the reflector I00 to produce parallel rays.

A direct current energy source I I5 is connected to the are light I05 through a current limiting energy source H5 through a current limiting re- Alternating current set up in the oscillatory circuit consisting of condenser I24 and inductor I25 may be used to apply an alternating voltage to the conductors I20 and I 2i through the inductive coupling between inductor I25 and an inductor I26. denser I2! is the inductor I26 and the conductor I20 to prevent inductor I26 from short circuiting the direct current source Illi.

In the operation of the transmitting system oi Fig. 8a, the are light I05 is continuously excited by a pulsating current formed by the superpositioning of the alternating current trom the Poulsen arc I22 on the direct current from the energy source H5. The amplitude of the alternating current in the arc I05 may be adjusted to any desired value by means of the resistor I23. but it is preferable that this amplitude be not large enough to make the current in the arc I05 ever reach a zero value. The light from are I05 does material of the elec-.

tionable feature.

Another advantage of the system of Fig. 8a is that the radiation tioned a loop III of suitable turns which may be rotated with reference to loops I25 and I36 and which impresses an alternating voltage on the conductors I20 and I2I'. The modulated light waves from the are light I28 are brought to a parallel beam by condensing lenses I20, then passed through a light fllter I40 of the same type 25 of Fig. 4 in that it passes the invisible light from light I05 and reflects the visible light from light I20. The superimposed light beams are reflected from a crystalline plate I42 of quartz. beryl, tourmaline, or the like. capable of causing "scattering with change in frequency", onto a light sensitive cell The reflections from associated therewith. This is deinput resistor I46. vacuum tubes I41 and I48, plate inductor I49, grid inductor I50, feed-back inductor I5I. tuning condenser I52, and by-pass condenser I53. The output terminals of the receiver I44 are connected to a reproducing device I54.

In utilizing the receiving system of Fig. 8b. the values of the resistors I32 and I33 are selected and the variable condenser I34 is adjusted so that the oscillatory currents from the arc I22 through the two loops I35 and I36 are 90 degrees out of phase. It is then possible by rotating the loop I31 with reference to loops I35 and I36 to change the phase of the current modulations in the arc I28 through 360 degrees. This phasing may then be adjusted so that the modulations of the transmitting source I05 and the local source I28 arrive at the reflecting plate I42 in-phase. Since the modulations of the source I05 are not interrupted, the adjustment of the loop I31 can be left fixed when communication has been established. No audible modulations have been specifically provided for in either the transmitting source I05 or the local source I28 so that the receiving circuit I44 is used to make the signals audible in the well known manner.

Figs. 9a and 9b show still another complete light wave communication system in which the transmitting light source is of novel form. the receiver light source and scattering" medium have temperature control, and both light sources are excited with pulsating currents of a dinerent type from those employed in the system of Figs. 8a and 8b. Fig. 9a is the transmitter and Fig. 9b the receiving equipment. In this system the reflectors I60, I6I, I62, and I63 are also similar to reflectors 30, 3I, 32, and 33 of Fig. 5. A transmitting light source I65 is of the gas discharge type and comprises a discharge chamber I66 containing suitable electrodes I61. Connected to this chamber is a plurality of radial arms I68 of glass tubing. or similar material that will pass the light waves of the frequency it is desired to use. The arms I68 may be fashioned in a manner to permit all light radiations given off by the arms to arrive at a point I68 in phase. The chamber I66 and the arms I68 contain gas or vapor at a pressure that will allow a glow discharge between the electrodes I61 to extend into the arms I68. This discharge tube is positioned inside of a chamber I10 in such a manner that the point I is at the center of a small aperture I1I in one face of the chamber. The chamber I10 is constructed so that a maximum amount of light from the arms I68 passes through the aperture wh ch is positioned at the focus of the reflector I60. A small opaque disk I12 may be so placed that no direct light from between the electrodes I61 passes through the aperture MI. The side elevation of light source I is shown in Fig. 10. I believe this specific form of light source is new and particularly adapted to my transmitting system.

The light source I65 is excited in a simple manner with pulsations of a suitable frequency by means of a source of direct current potential I13 acting through conductors I14 and I15, an adjusting resistor I16, and a keying resistor I11. A variable condenser I18 between the conductors I14 and I15 serves to adjust the frequency of the pulsations. Across the resistor I11 are connected a back contact I and an arm I8I of a suitable keying relay I82. The relay I82 is operated by a potential source I83 in accordance with the operation of a signalling device I84.

When the signalling device I84 is closed and the contact I80 disconnected from the arm I8I, a pulsating current will flow between the electrodes I61 due to the negative voltage-current characteristic of the gas in the chamber I66 and the charging and discharging effect of condenser I18. These pulsations. being explosive in character, will shock excite the light emitting electrons and cause the radiation of wave trains at periodic intervals. The frequency of the pulsations can be controlled by various means, such as by the adjustment of the condenser I18 and resistor I16. When the arm I8I touches contact I80 due to the opening of the signalling device I84, resistor I11 is shorted and the current passing between electrodes I61 increases to a value that will either not permit the occurrence of pulsations or will permit pulsations of a much lower frequency. The radiations emitted by the light source I65 will. therefore. change from an irregular and inefiicient type when the signalling device I84 is open to a regular and efficient type when the signalling device I84 is closed.

The local light source in Fig. 9b consists of one or more discharge tubes I85 capable of giving off light of the desired frequency and positioned in such a manner as to uniformly illuminate the vertical walls of a container I86 for a gaseous, liquid, or solid scattering medium I81. The container I86 may be arranged to maintain desired pressures on the medium I81 and its walls may be of glass or some material that will readily pass light of the local source frequency and of the shifted frequency. The lights I85 are positioned in a liquid bath I88. the temperature of which is maintained at a value that will result in most efficient scattering" of the local light waves by means of a temperature control device I88 acting through a circulating coil I80 in the well known manner. The liquid I88 may be a substance or combination of substances that will serve the same purpose as the filter 18. A light filter I9I similar to filter 80 admits only light of the desired frequency from the reflector I63 into the top of the scattering" medium I81. A spot I92 in the scattering medium I81 is focused through a light filter I83 similar to filter 84 onto a light sensitive cell I94 by a suitable lens I95.

The discharge tubes I85 may be connected either in parallel, as shown, or in series, and excited in a manner similar to the light source I65 in Fig. 9a. The circuit elements used for this purpose include conductors I86 and I81, a variable condenser I98, 9. source of direct current potential I83. an adjusting resistor 200, and a vacuum tube 20I. The plate to filament resistance of the vacuum tube 20I may take the place of the resistor I11 in Fig. 9a. In an output lead 202 of the cell I94 is connected an inductor 203 which is suitably coupled to a tuned circuit including inductor 204 and variable condenser 205 and which is connected to an amplifier 206. The amplifier 206 may be of any well known type and may include suitable filter circuits. An output inductor 201 of the amplifier 206 is suitably coupled to an inductor 208 in the input circuit of the tube 20I which includes a variable condenser 209 and a variable resistor 2I0. The resistor 2I0 is suitable for adjusting the phase of the voltage impressed on the grid of the vacuum tube 2II to a desired value. A suitable receiver 2 is connected to the cell I94 through conductors 202 and 2I2. The signals detected by the receiver 2II are understood by means of a reprodu ing device 2I3.

In using the system of Fig. 9b, the frequency of the pulsations in the light sources I55 is adjusted by means of condenser I53 and resistor 230 to the desired value. preferably the same as in the transmitting light source I55. The resistor 213 may then be adiusted so that the pulsations in the light waves from the lights I arrive at the scattering" medium I81 in-phase with those from the transmitting source I55. Once this adjustment has been made, the pulsations from the light sources I55 and "5 will be automatically pulled into the desired phase through the action of the inductor 203 on the amplifying system for the vacuum tube 20! in a manner similar to that in Fig. 6b and for the same purpose.

Figs. 11:: and 11b show respectively a transmitting and receiving system for still another communication system embodying the principles of the invention and in which light sources of a self oscillatory type are employed. In this system, reflectors 220 and 22! operate in a manner similar to reflectors 30 and 3| of Fig. 5. but may be of a form specifically adapted to the other elements of this system. A transmitting light source 225 positioned at the focus of the reflector 220 is a gas discharge tube of the hot cathode type, the

gas pressure of which is suitable for maintaining oscillations in the tube in a manner described hereinafter. Fig. 12 shows an enlarged side elevation of one form of the light source 225. It comprises a spiraled glass tube 225 having on its ends chambers 221 and 22B and containing suitable gas or vapor at the desired pressure. Chamher 221 contains a suitable anode 223 and chamber 228 a suitable cathode 230 which may be heated by a heater coil 23i. A connection from anode 229 is made with conductor 232. from cathode 230 with conductor 233, and from heater coil 23l with conductors 234 and 235.

The light source 225 may be energized from a source of direct current potential 235 acting through the conductors 232 and 233, a modulating source 231, and a variable resistor 238. The resistor 238 is employed to vary the meat flowing through the discharge tube 225. but may be omitted if suitable voltage control means are provided in the potential source 235. A by-pass condenser 239 may be used to keep oscillatory current out of the potential source 235. The heater coil 231 may be energized by any suitable potential source, such as an alternating current generator 241 acting through the conductors 234 and 235 and a variable resistor 242. The resistor 242 may be of any value suitable for adjusting the temperature of the cathode 230 to the desired value.

It has been found possible with a circuit arrangement such as that shown in Fig. 110 to obtain oscillations within the gas of the discharge tube 225. the frequency of which depend mainly on the pressure of the gas in the tube 225 and the temperature of the cathode 230. This frequency may be independent of the amplitude of the current flowing through the tube. The light radiated from the spiraled tube 225, therefore, varies in accordance with these oscillations in the gas. By varying the amplitude of the current through the tube 225 with the modulating source 231. the light radiations will be modulated in accordance therewith.

A local light source 245 for the receiving system of Fig. 11!) is also of the hot cathode type and is detailed in the enarged section of Fig. 13. in which 245 is a chamber of insulating material containing a cathode 241 and its heater coil 243 with external connections 243. 255, and 251 respectively. Attached to the chamber 245 is a tube 252 also of suitable insulating material, but not necessarihz transparent. one end of which is turned back to a ring 253. Attached to the chamber 245 and surrounding the tube 252 is an anode chamber 254 made of filter glass or any suitable material that will readily pass light of the local light frequency. In this chamber is an electrode 255 connected to an external conductor 255. the electrode being so shaped as to permit a uniform gas discharge throughout the chamber 254. The chamber 254 is made in such a form and attached to the chamber 245 in such a manner that gas or vapor can be maintained at a suitable pressure within the chambers 245 and 254 and permit a uniform gas discharge to pass from the cathode 241 through the tube 252 to a point 251 and back through the chamber 254 to the anode 255. Surrounding an end of the chamber 254 is a scattering" chamber 258 containing a suitable "scattering" medium 255 at a desired pressure and made of filter glass or any material that will readily pass the invisible radiations from source 225 and the shifted light waves used to control a light sensitive cell 250. The light source 245 may be positioned with reference to the reflector 221 so that the maximum amount of radiations from the source 225 strike the surface of the "scattering" chamber 258. The cell 250 may be positioned with reference to the scattering" chamber 253 so that the maximum number of the shifted light waves may be focused on the cell 250 by a lens 25! through a light filter 252. This specific form of structure for the local light source and scattering medium permits emcient utilization of the radiations from the transmitting source 225.

The light source 245 may be energized in a manner similar to source 225 by a direct current potential source 253 acting through the conductors 249 and 255. a resistor 254. and an inductor 255. The heater coil 248 may be energized by a potential source 255 acting through the conductors 250 and 25l, and a resistor 251. The

cell 250 is connected through conductors 258 and 255 and an inductor 210 to a suitable receiver 211 which actuates a reproducing device 212. Inductor 215 is suitably coupled to an amplifying and phase shifting system similar to that in Fig. 9b comprising inductor 213, condenser 214. ampllfler 215, inductors 215 and 211, condenser 218. resistor 21!, vacuum tube Ill, condenser 281, inductor 232, potential source 233, and by-pass condenser 234.

In the operation of the system of Fig. 11b, the excitation frequency of the light source 245 may beadiustedtotheaamevalueasthat ofthe source 225 by the resistor 251 and allowed to oscillate continuously while signals are being sent. The oscillations in aoin-ce 225 may also be continuous, but in order to make sure that the oscillations in both light soin'ces will continue at the same frequency and with the desired phase relationship the amplifying and phase shifting system coupling inductor 214 with inductor 255 is provided. This system serves the same purpose and functions in the same manner as the corre- D nding System in Fig. 9b.

Pigs. 14a and 14b show respectively a plural channel transmitting and receiving system in accordance with my invention and in which light sources of the electrodeleas type are employed. In this system the reflectors 230, 251. 292. and 253 are also similar to reflectors 30, 31, 32. and 33 of Fig. 5. In Fig. 1M. a transmitting light source 236 positioned at the focus of the reflector 290 differs from light sources previously described in other embodiments of my invention in being of the electrodeless type. It is well known that the electric field in a discharge tube employing electrodes varies in intensity from one electrode to another, especially in the vicinity of the cathode. In an electrodeless discharge the field is uniform so that the light radiations are more uniform throughout the entire discharge. While the other forms of light sourcm described hereinabove may be employed for communication with plural channels. the electrodeless type is particularly well adapted for the purpose. as will be shown hereinafter. A form in which the light source 236 may be used is shown schematically in side elevation in Fig. 15. A tubular ring 296 made of glass. or some other material suitable for passing light of the desired frequency. contains one or more gases at a pressure suitable for permitting an electrodless discharge of a desired light frequency and intensity when under the influence.

of an alternating electric field. The intensity of the light radiated from the ring 236 is preferably proportional to the magnitude of the electric field. On the ring 286 may be wound one or more windings 291. 26!. and 299 arranged in such a manner that light from the ring 296 may readily pass between turns of the windings. While this form of light source is preferred. other possible forms will be apparent to those skilled in the art.

Referring to Fig. 14a. winding 2" may be energized by a suitable excitation source 30!! acting through a transformer 30l. a variable condenser 302. and conductors 303 and 304. The energy from the excitation source 300 may be unmodulated and of an audible frequency. if desired. The winding 296 may be energized by an excitation source 305 acting through transformer 306, variable condenser 306, and conductors 303 and 3B9. Source 305 may be of a different frequency from source 300 and may be modulated by a suitable source 3l0. In a similar manner.

.excitation source 3. of a different frequency from sources 300 and 305 and modulated by a source 3l2. may be used to excite the winding us through a transformer 3l3, variable condenser 3l4, and conductors 303 and 3l6.

In the operation of the system of Fig. 14a, excitation source 300 may be used to continuously excite the gas in the tube 296 in any well known manner. This will keep the gas in condition to respond instantly to any variations in the amplitude of the currents from sources 305 and 3. The frequency of the currents from sources 305 and 3 may be high since an electrodeless discharge functions best on very high radio frequencies. The wave radiations given off by the light source 266 will. therefore. vary in intensity in accordance with the combined efi'ect of the unmodulated alternating current from the source 300 and the modulated high frequency currents from the sources 305 and 3| l.

A local light source 3l6, shown in section in Fig. 14b. may also be of the electrodeless discharge type and consist of a ring 3" of rectangu lar cross-section containing one or more suitable gases 3" and surrounded by concentric windings 3", 320. 32l. and 322. The ring 3|! may be of glass or any material suitable for maintaining a desired pressure on the gases 3" and also for passing light of the desired frequency from the gases 3|! into a "scattering" medium 323, such as a suitable liquid or gas, which may be mainaosasaa tained at a definite pressure. A tubular light filter 324 may be used between the ring 3|! and the "scattering" medium 323. Radiations from the transmitting source 235 pass from the refiector 293 through a light filter 325 into the medium 323. Light of shifted frequency in a suitable spot 326 in the medium 323 is focused by a lens 321 through a light filter 32! onto a light sensitive cell 326. The cell 323 may be connected through conductors 336 and 33! to a direct current potential source 332, variable condenser 333. variable resistor 334. transformer 33$. variable condenser 336. transformer 331. variable condenser 338. and transformer 333. The current variations through the cell 323 are induced through the transformer 335 into an amplifier 3 which in turn excites the windings 3i! and 322 through a transformer 342 and a variable condenser 343. The amplifier 3 may contain filters. tuned circuits and other elements needed to select and amplify currents of the same frequency as the excitation source 300. The current variations through the cell 326 are also induced through the transformer 33! into an amplifier 345 which may contain filters. tuned circuits. and other elements suitable for selecting and amplifying the modulated frequency from a source such as 305. By means of a transformer 346 the amplifier 346 excites the winding 32l. in parallel with a variable shunting condenser 341. through conductors 343. a variable condenser 360. and the primary of a transformer 352. A suitable receiver 363 with a reproducing device 354 is connected to the secondary of the transformer 352. In a similar manner. transformer 33! is connected to another amplifier 361 which may select and amplify the modulated frequency from the source 3i I. By means of a transformer 356 the modulated alternating currents of this frequency are used to excite the winding 320. in parallel with a variable condenser 333. through the coupling circuit comprising conductors 360. variable condenser 362. and the primary of a transformer 364. A receiver 365 with its reproducing device 366 is connected to the secondary of the transformer 364.

In the operation of the receiving circuit of Fig. 14b. the gases 3" in tube 3". when excited by windings 3", 320. 32l. or 322, transmit light waves into the medium 323 from all sides thus permitting very efficient "scattering" of the light waves. The intensities of the light waves are determined by the combined effects of the windings 3l8. 320. 32l. and 322 so that the amount of light of shifted frequency projected onto the cell 328 depends both on the intensity of the light from the gases 3|! and on that from the transmitting source 285. This provides a regenerative effect which permits the utilization of transmitted light waves of relatively low intensities. To obtain this effect it is desirable to keep the gases 3|! at least partially excited all the time and this may be accomplished through the unmodulated excitation of source 300 and the amplifier 3. Two windings. 3" and 322. are used with amplifier 34! on account of the lower excitation frequency employed and to keep the gases in the ring 3ll imiformly excited. The phase of the current fed by the amplifier 3 into the windings 3|! and 322 may be adjusted to a desired value by means of the resistor 334. When light wave modulations from another source. such as source 305. reach the scattering medium 323. the amplifier 345 quickly builds up the oscillatory current in the circuit connecting it with the winding 32! due to the regenerative action described above. The amplitude of the oscillatory current in this circuit will increase and diminish in accordance with the variations of the modulating source 310 and these variations will be induced through the transformer 352 into the receiver 353. The phase of the current in the winding 32! may be adjusted by means of the condenser 341, the proper adjustment being indicated in this case by maximum response from the reproducing device 354. When both sources 305 and 3| l are used, amplifiers 345 and 351 will each select and amplify only one frequency so that only the signals from modulating source 3| 0 will be obtained in reproducer 354 and only the signals from modulating source 312 will be obtained in reproducer 366. While I have shown only two communication circuits in this embodiment of my invention, it is to be understood that more circuits may be employed, if desired, by the addition of similar elements.

Many modifications of my improved system of communication will be apparent to those skilled in the art and my invention, therefore, is not to be restricted to the specific embodiments chosen for purposes of illustration, but is to be limited only by the scope of the appended claims.

What I claim is:

1. In a detecting system for vibrations of visible and invisible light-frequencies and frequencies adjacent thereto, a local source of vibration, means independent of said vibrations to be detected for scattering with change in frequency at least a portion of said local vibrations, and means for increasing and decreasing said scattered vibrations of changed frequency with said vibrations to be detected.

21 In a detecting system for invisible and inaudible vibrations, a local source of vibrations, scattering means independent of said invisible and inaudible vibrations for shifting the frequency of at least a portion of said local vibrations to at least one frequency in the visible spectrum, and means for increasing and decreasing the intensity of said shifted vibrations with said invisible and inaudible vibrations.

3. In a signalling system, plural means for generating variable intensity light vibrations having diiferent frequencies, and means actuated by the vibrations of one frequency from one of said generating means and also by the vibrations of a second and different frequency from a second of said generating means to produce by scattering with change in frequency light vibrations of a third and different frequency, said light vibrations of said third frequency indicating directly the variation in the vibrations of at least one of said first and said second frequencies.

4. A signalling system in accordance with claim 3 in which said last mentioned means includes a scattering medium for shifting the frequency of a portion of said light vibrations of said first frequency.

5. In a signalling system, an oscillator, a source of light waves energized by said oscillator, a medium upon which said light waves are directed for shifting the frequency of at least a portion of said waves. a second light source. irradiations therefrom being directed on said medium for varying the intensity of said shifted frequencies, said second light source being energized at a certain rate. and means for maintaining said oscillator in a predetermined phase relationship with respect to the energization of said second light source.

6. In a signalling system. a source of variable intensity invisible light waves, a source of light waves lying within a portion of the visible spectrum. a scattering medium for shifting the frequency of at least a portion of said visible light waves, said shifted portion indicating directly the intensity variation of said invisible light waves, and means for directing the light waves from both of said sources on said medium.

7. In a communication system of the class described, a source of wave vibrations lying above 7x10 cycles per second, means for modulating said vibrations. a second source of wave vibrations lying above 7x10 cycles per second, scattering means independent of said first wave vibrations for shifting at least a portion of said second wave vibrations to wave vibrations of different frequencies than said second wave vibrations, means for varying at least one of said vibrations of shifted frequency directly with said modulations of said first source, and means for detecting said variations in said vibrations of shifted frequency.

8. A communication system in accordance with claim 7 in which said scattering means is a solution of carbon tetrachloride and said detecting means is a photo cell sensitive to said shifted vibrations.

9. The method of detecting invisible vibrations comprising shifting by scattering and independently of said invisible vibrations the frequency of certain other vibrations above the radio spectrum to at least one frequency in the visible spectrum, and modulating said shifted vibrations with said invisible vibrations, said modulations being in phase with the modulations of said in visible vibrations.

10. The method of communication between separated stations comprising projecting light vibrations between said stations. modulating said vibrations at one of said stations, shifting the frequency of local light vibrations by scattering at the receiving station, increasing and decreasing the intensity of said vibrations of shifted frequency with said modulated light vibrations, and detecting the variations in said intensity.

11. The method of signalling from one station to another comprising projecting modulated invisible light waves between stations, generating visible light waves at the receiving station, shifting the frequency of at least a portion of said visible light waves by scattering, varying said light waves of shifted frequency in direct accordance with the modulations of said invisible waves, and detecting the variations in said light waves of shifted frequency.

12. In a signalling system, means for generating high frequency impulses of invisible light waves, means for concentrating said waves at a distant point, and means at said distant point for translating said impulses into impulses of visible waves, said translating means comprising a second source of corresponding light wave impulses, scattering means controlled by said invisible wave impulses for shifting the frequency of at least a portion of said light wave impulses from said second source, and means for detecting the variation in said light wave impulses of shifted frequency.

13. In combination. an oscillator, a light d scharge tube, means for actuating said tube with said oscillator, means for modulating said oscillator, a beam projecting device for directing the light waves of said tube to a beam concentrating device, a light scattering medium, a second light source, a second oscillator maintained in synchronism with said first oscillator for actuating said second source, means for directing both of said light waves on said scattering medium, and means focused on said medium for detectin the presence of said first light waves.

14. In combination, a source of inaudible v'ibrations, means for modulating said vibrations, means for concentrating said vibrations at a distant point, an independent source of vibrations at said distant point, a frequency shifting medium for shifting the frequency of the vibrations of said independent source, means for directing the vibrations of said sources to said medium, means for detecting the presence of said shifted frequencies when varied directly with said inaudible vibrations, and means for interrupting the vibrations of said independent source at an audible rate.

15. In combination. a source of modulated invisible light waves, means for concentrating said waves at a distant point, an independent source of light waves at said distant point, scattering means for changing the frequency of at least a portion of the light waves of said independent source to a frequency in the visible spectrum. means for directing said invisible waves to said scattering means. and means for observing the modulations of said light waves of changed frequency by said invisible waves.

16. In a system for detecting high frequency vibrations of a certain value from a distant point, a local source of high frequency vibrations of a different value, a scattering medium surrounding at least a portion of said source for changing the frequency of at least a portion of said local vibrations, 9. containing structure for said medium, means for directing said first mentioned vibrations through said structure, and means directed through said structure for detecting intensity variations of said vibrations of changed frequency set up by said first mentioned vibrations.

17. In a signal detecting system, a high fre quency vibration source of a certain frequency, a medium for shifting at least a portion of said vibrations to another frequency, means for transla ting said shifted vibrations into electrical ourrents. an energy 'suissiy for said high frequency vibration source. and means for controlling the energy supplied to said high frequency source by said tramiated currents.

18. In a signalling system, an oscillator, a source of light waves energized by said oscillator, a medium upon which said light waves are directed for shifting the frequency of at least a. portion of said waves. a second light source, irradiations therefrom being directed on said medium for varying the intensity of said shifted frequencies in direct accordance therewith, said second light source being energized at a certain rate, and means for maintaining said oscillator in a predetermined phase relationship with respect to the energization of said second light source.

19. In a signalling system, an oscillator, a source of light waves energized by said oscillator, means for modulating said oscillator, a beam projecting device for directing said light waves to a beam concentrating device, a light scattering medium, means for directing said light waves from said beam concentrating device on said medium, a second oscillator, a second light source energized by said second oscillator, means for directing light waves from said second source on said medium to permit the scattering with change in frequency of at least a portion of said light waves, means for detecting the intensity variations in said scattered light waves set up by said modulating means, and means for adjusting the maximum intensity of said variations, said means comprising frequency and phase adjusting elements for said second oscillator.

20. In a signalling system, a source of variable intensity invisible light waves. a source of light waves lying within a portion of the visible spectrum, a medium scattering for shifting the frequency of at least a portion of said visible light waves, the intensity of said shifted portion indicating directly the intensity variation of said invisible light waves, means for maintaining said medium at a definite pressure, and means for directing the light waves from both of said sources on said medium.

21. In a signalling system. a source of variable intensity invisible light waves, a source of light waves lying within a portion of the visible spectrum, a medium scattering for shifting the frequency of at least a portion of said visible light waves,.the intensity of said shifted portion indicating directly the intensity variation of said invisible light waves, means for maintaining said medium at a definite temperature, and means for directing the light waves from both of said sources on said medium.

22. In a signalling system. a source of invisible light waves, a source of light waves lying within a portion of the visible spectrum, a medium for transferring at least a portion of the energy in said invisible waves to said visible waves for increasing the frequency of at least a portion of said visible waves, said increased frequency portion indicating the intensity variation of said invisible light waves, and means for directing the light waves from both of said sources on said medium 23. The method of synchronizing separated oscillators comprising translating at least a portion of the energy of one of said oscillators into modulated light vibrations of a particular frequency, shifting at least a portion of said modulated light vibrations to modulated light vibrations of a different frequency, translating at least a portion of the energy of a second of said oscillators into modulated light vibrations of a difierent frequency from said first and said second light vibrations, intensifying said second I light vibrations with said third light vibrations, translating the modulations in said second and shifted light vibrations into electrical vibrations and impressing said electrical vibrations on said first oscillator to maintain the frequency of said first modulations the same as the frequency of said third modulations.

24. In a synchronizing system, an oscillator, a source of light waves energized by said oscillator. a medium for shifting the frequency of at least a portion of said waves, a second oscillator of substantially the same frequency as said first oscillator, a source of light waves energized by said second oscillator increasing the intensity of said shifted frequencies, means for translating the variations in said shifted frequencies into electrical currents, and means for impressing said electrical currents on said first oscillator to maintain the oscillations therein at the same frequency as the oscillations in said second oscillator.

25. In a synchronizing system, an oscillator, a source of light waves energized by said oscillator. a medium for shifting the frequency of at least a portion of said waves, a second oscillator of LUUi lulu...

substantially the same frequency as said first oscillator, a source of light waves energized by said second oscillator increasing the intensity of said shifted frequencies, means for translating the variations in said shifted frequencies into electrical currents, means for impressing said electrical currents on said first oscillator to maintain the oscillations therein at the same frequency as the oscillations in said second oscillator, and means for adjusting the phase between said first and said second oscillators.

26. In combination, a light source, means for energizing said source, means for modulating the light waves from said source, means for changing the intensity of the light waves from said source at a frequency different from said modulating means, a beam projecting device for directing the light waves from said source to a beam concentrating device, a light scattering medium, a second light source, means for energizing said second source, means for modulating the light waves from said second source in a manner similar to said first modulating means, means for adjusting the phase between said first modulations and said second modulations. means for directing said light waves from said beam cencentrating device and said second source on said scattering medium. and means focused on said medium for detecting the effect of said intensity changes on said medium.

27. In combination, an oscillator, a light discharge tube, means for actuating said tube with said oscillator, means for modulating said oscillator, a beam projecting device for directing the light waves of said tube to a beam concentrating device, a light scattering medium, means for maintaining said medium at definite physical conditions, a second light source, a second oscillator maintained in synchronism with said first oscillator for actuating said second source, means for directing both of said light waves on said scattering medium, and means focused on said medium for detecting the presence of said first light waves.

28. In combination, an oscillator, a light discharge tube, means for actuating said tube with said oscillator, means for modulating said oscillator, a beam projecting device for directing the light waves of said tube to a beam concentrating device, a light scattering medium, a second light source, a second oscillator maintained in synchronism with said first oscillator for actuating said second source, means for adjusting the phase of said second oscillator with respect to said first oscillator, means for directing the light waves from said beam concentrating device and from said second light source on said scattering medium, and means focused on said medium for detecting the presence of said first light waves.

29. In a signal detecting system, a high frequency vibration source of a certain frequency, an

alternating energy supply for said source modulating said vibrations, a medium for shifting at least a portion of said modulated vibrations to another frequency, means for translating said shifted vibrations into alternating electrical currents, means for controlling the energy supplied to said high frequency source by said translated currents, said controlling means including means for adjusting the phase between said translated currents and said alternating energy supply.

30. In a transmission system, a beam projecting device, a light discharge tube having extensions therefrom, means for energizing said tube, means for setting up travelinglight pulsations in said extensions, means for interrupting said pulsations, an enclosing structure for said tube, a diaphragmin said structure situated at the focus of said beam projecting device, said tube and said extensions being positioned with respect to said diaphragm to permit the pulsating light waves therefrom to reach said diaphragm substantially in phase.

31. In a communication system, a light discharge tube, a pluralimgitation sources for said tube, means for separa e y modulating at least one of said sources, a beam Wtifig'device for directing light waves from said tube to a beam concentrating device, a light scattering medium, means for directing said light waves from said concentrating device on said medium, a second light discharge tube, a plurality of excitation sources for said second tube, means for directing light waves from said second tube on said scattering medium, means focused on said medium for detecting the light modulations in said first tube, and means for separating said detected modulations in accordance with said separate modulating means.

32. In a signalling system, a medium for light scattering with shift in frequency, means for focusing invisible light waves on said medium, a local light discharge tube, means for energizing said tube, means for directing visible light waves from said local tube on said medium, and means for detecting the relative intensities of light waves of shifted frequency from said medium, said intensities varying directly in accordance with said focused invisible light waves.

33. In a signalling system, a medium for light scrattering with shift in frequency, means for focusing invisible light waves on said medium, a local light discharge tube, means for energizing said tube, means for directing visible light waves from said local tube on said medium, means for filtering out undesired components of light waves of shifted frequency from said medium, and means for detecting the relative intensities of said filtered waves of shifted frequency, said intensities varying directly in accordance with said focused invisible light waves.

HERMAN POTIS MILLER, JR. 

